1. The Field of the Invention
The present invention relates to an automotive air conditioning system. In more particular, the present invention relates to systems, methods, and apparatus, for utilizing deceleration of an automotive engine to compress refrigerant in an air conditioning system.
2. The Relevant Technology
For the past several decades, air conditioning systems have been used in automobiles and other motor vehicles during hot weather to provide more comfortable conditions for drivers and other occupants of the motor vehicles. Traditional air conditioning systems utilize a refrigerant to cool and/or dehumidify air. The cool air is then dispersed into the passenger compartment in a manner so as to mitigate the temperature in the passenger compartment.
Traditional automotive air conditioning systems draw the power to compress the refrigerant from the engine of the motor vehicle. In one configuration, an engine fan belt pulley is connected to the engine and to the compressor of the air conditioning system. When it becomes necessary to further compress the refrigerant in the air conditioning system, a clutch (e.g., a magnetically operated clutch—“magnetic clutch”) provides engagement between the compressor and the fan belt pulley. Engaging the magnetic clutch allows the fan belt pulley to provide power to the air conditioner compressor from the engine, effectively compressing the refrigerant in the system.
For example, when an air conditioner is switched to an “on” position to cool the motor vehicle's interior, the magnetically-operated clutch provides an effective engagement between the compressor and the fan belt pulley. This translates power from the engine, allowing the compressor to operate and compress the refrigerant. Once compressed to a pre-set pressure level, the compressor is disconnected from the engine, such as by disengaging the magnetic clutch. The air conditioning system then passes the compressed refrigerant through a condenser/heat exchanger and, thereafter, to an expansion valve, orifice tube, or other mechanism in the air box heat exchanger. In the air box heat exchanger, the compressed refrigerant is expanded and liquefied to thereby cool incoming air. The fresh air, once cooled, is directed into the car's interior.
Typically, a high and/or low pressure switch is utilized to identify the pressurization of the refrigerant in the air conditioning system. Pressurization of refrigerant in the air conditioning system allows for desired expansion of the refrigerant in the air box heat exchanger to cool air. Before the refrigerant passes into the air box heat exchanger, such as in the compressor or tubing between the condenser/heat exchanger and the air box heat exchanger, the refrigerant is in a high pressure state. This is often referred to as the high pressure side of the system. When the refrigerant passes into the air box heat exchanger and before being recompressed in the compressor, the refrigerant is in a low pressure state. This is often referred to as the low pressure side of the system.
The configuration of most air conditioning compressors does not require continuous actuation of the magnetic clutch, the engine fan belt, or other sources of power for the compressor. In particular, during operation of the air conditioner, operation of the heat exchanger generally needs only intermittent operation of the magnetic clutch/compressor. As the volume of refrigerant is being expanded and passed into the low pressure side of the system, the transfer of refrigerant to the low pressure side of the system increases the pressurization on the low pressure side of the system. Similarly, the volume of refrigerant that is being held on the high pressure side of the system decreases. The decrease in the volume of refrigerant decreases the pressurization of refrigerant on the high pressure side of the system.
Of course, the decrease in the pressurization on the high pressure side of the system can decrease the efficiencies of operation of the air conditioner. For example, the refrigerant may not provide optimized cooling of air in the air box heat exchanger. The state of pressurization of the refrigerant can thus be detected in a number of ways. In one conventional system, the pressurization of the refrigerant on the low pressure side of the system is monitored as an indicator of the pressurization of the refrigerant on the high pressure side of the system. For example, when the pressurization of the refrigerant on the low pressure side of the system increases to a certain level, the pressurization of the refrigerant on the high pressure side of the system is deemed to have decreased below desired levels.
When the refrigerant on the low pressure side of the system has reached certain upper pressure limits, the magnetic clutch is engaged and power from the engine is translated to the compressor. Refrigerant pulled from the low pressure side of the system is compressed by the compressor to increase pressurization of the refrigerant on the high pressure side of the system. Once the pressurization of the refrigerant on the low pressure side of the system has been reduced by operation of the compressor, the magnetic clutch is disengaged, and the engine is allowed to operate without the increased load required to drive the engine fan belt pulley.
The increase in pressurization of refrigerant on the high pressure side of the air conditioning system allows the refrigerant to be useful as it flow through the condenser/heat exchanger. In particular, the compressed refrigerant continues cooling even when the engine fan belt pulley is not in engagement with the compressor. Ultimately, however, the continual flow of refrigerant and cooling of air in the heat exchanger also results in a gradual decline in pressurization of the refrigerant in the air conditioning system.
When the refrigerant pressure reaches a preset high pressure value on the low pressure side of the system (i.e., depleted high pressure side), the low pressure side limit switch again turns the magnetic clutch back on, allowing the compressor to once again draw power from the engine pulley, and increase the pressurization of the refrigerant on the high pressure side of the system. When the refrigerant reaches the preset low pressure value on the low pressure side of the system, the low pressure limit switch again disengages the magnetic clutch and the compressor from the engine pulley.
Since the depressurization of refrigerant on the high pressure side is gradual, the ongoing air conditioning can continue to run for some time without applying a load on the motor vehicle engine. While this provides efficiencies in system operation, a number of deficiencies are also presented. For example, because the air conditioning system does not apply a continuous load to the motor vehicle engine, the default operating state of the motor vehicle is typically one in which the engine fan belt pulley is not in operation. Thus, motor vehicle engines are often designed to optimally operate in the absence of running of the engine fan belt pulley. As a result, during certain operating conditions, it can be disadvantageous for the air conditioning system to exert a load on the motor.
For example, typical compressors of air conditioning systems may not be actuated when the motor vehicle is idling, or when the temperature of the engine has exceeded certain upper temperature limits. Instead, the compressors of conventional air conditioning systems are configured to operate when the motor is in a state of acceleration or at a constant driving speed. During acceleration, increased load on the engine is expected as part of the acceleration process. While engaging of the engine fan belt pulley during acceleration may place an increased load on the engine of the motor vehicle, such increased load is typically minimal compared to the load placed on the engine during acceleration.
In other words, the design requirements which allow for acceleration of the motor vehicle engine also tends to accommodate the increased load needed to drive the engine fan belt pulley, and charge the air conditioning compressor. While utilizing acceleration cycles to power the air conditioning compressor does not present challenges in operation of the motor vehicle engine, the additional engine load imparted by the air conditioning compressor can nonetheless represent significant fuel consumption increases when compared with engine operation in the absence of such additional load.
For example, in some situations, depending on the specific heat load encountered during operation of the air conditioning system, operation of the air conditioning compressor can result in about 20-25 percent or more reduction in overall vehicle fuel efficiency (e.g., mpg, kpl, etc.) Such energy consumption implications can not only limit the fuel efficiency of the motor vehicle, but can also be quite costly when the air conditioning system is used over a period of weeks or months. Additionally, such additional energy consumption results in the burning of additional fossil fuels which correspondingly increases the total combustion exhaust expelled by the motor vehicle during operation.